Acoustic vibration generator

ABSTRACT

The invention relates to an arrangement for generating sound waves or anti-sound waves. For the sound waves. For the sound wave transducer, use can be made of window glass (1) or other types of transparent material, which is set into vibration by means of one or a plurality of actuators (6), such as piezo elements or actuators based on electrostatic attraction and repulsion.

The invention relates to an arrangement for effecting acousticvibrations in a medium, for instance air, at least comprising asubstantially sheet-shaped body for transmitting the vibrations to themedium, provided with at least one actuator that can be connected to asignal generator.

DISCUSSION OF THE BACKGROUND

Arrangements of this sort, also called sound generators, aresufficiently well-known in the art, particularly owing to theirapplication as loudspeaker for playing music. A sound generator can,however, also be used for generating anti-sound. Sound waves acting fromoutside sources on an enclosed space can often be effectively attenuatedby recording these waves with a sound recorder and by subsequentlytransmitting them in phase opposition to a sound generator.

SUMMARY OF THE INVENTION

The object of the present invention is to integrate in an inventivemanner a sound generator in a windowpane, in particular for applicationin a building, but also in a vehicle or a vessel. Instead of or inaddition to window glass, use is also made of transparent syntheticmaterials which can be applied as a thin layer of foil. The advantage ofthis is that most buildings contain plenty of window glass or suchlikematerials which, owing to their flexibility, are excellently suitablefor generating acoustic vibrations. Use can be made of window glass orsuchlike materials which is for instance on the outside provided with amirror coating in order to exclude disturbing sunlight or to preventpeople from looking in. The use of window glass or suchlike materials assound generator eliminates the necessity to incorporate loud speakers.

In order to realize the above inventive principle, said arrangement ischaracterized in that the at least one substantially sheet-shaped bodycomprises at least one surface that is substantially transparent tovisible light in one or two directions.

An advantageous embodiment is based on double-glazed windows which arewidely used for their insulating properties. This offers possibilitiesfor incorporating, in a simple manner, the required actuator(s) in awindow.

This exceptional embodiment of the arrangement according to theinvention is thereto characterized in that the at least one bodycomprises two substantially parallel windowpanes which enclose a certainspace.

In this case, one windowpane preferably has a substantially highervibrational rigidity than the other windowpane. Thus, a directionalsensitivity is realized. The generated acoustic vibrations are thensubstantially transmitted on the side of the windowpane having lowvibrational rigidity. The windowpane combination can then be fitted in ahouse or building such that the window having low vibrational rigidityis on the inside.

In the embodiment comprising two parallel windowpanes, an actuator cannow be added in a simple manner by applying an electrically conductivelayer to both windowpanes, for instance in a vapour deposition process.By applying a voltage difference over both layers that varies with thesignal strength supplied by the electric signal generator, the twowindowpanes will either repel or attract one another, depending on thesignal shape applied. The amplitude of the voltage difference shall besufficiently high, generally in the order of kilovolts.

An advantageous embodiment is thereto characterized in that the twowindowpanes are at least partially provided with an electricallyconductive layer, which two electrically conductive layers incombination constitute the actuator during the creation of a voltagedifference between the two layers.

In a further advantageous embodiment comprising two parallelwindowpanes, a piezo element is used as actuator. By positioning thepiezo element in the space between the two windowpanes and mechanicallyconnecting the element to both windowpanes, an actuator is obtainedwhich, in combination with the two windowpanes, is capable of realizinga high sound pressure level.

This embodiment is thereto characterized in that the actuator comprisesa piezo element positioned in the space between the two windowpanes,which piezo element is mechanically connected to both windowpanes.

In a further favourable embodiment comprising two parallel windowpanes,the actuator is realized by a gas confined in the space between thewindowpanes. This embodiment is thereto characterized in that in thatthe space contains a gas which constitutes the actuator and in that aconnecting line is provided to connect the space with a pneumatic signalgenerator.

Instead of a gas, a liquid can also be used as actuator. This embodimentis thereto characterized in that the space contains a transparent liquidwhich constitutes the actuator and in that a connecting line is providedto connect the space with a hydraulic signal generator.

In order to make use of the glass panes of which there are plenty inmost buildings, an advantageous embodiment is characterized in that theat least one body comprises at least one sheet of glass.

The arrangement according to the invention is pre-eminently suitable forgenerating anti-sound vibrations. This embodiment is in particular beingapplied in buildings located in the vicinity of airports or motorways.This advantageous embodiment is thereto characterized in that theactuator is connected to a signal generator which is provided with meansfor generating anti-sound vibrations.

BRIEF DESCRIPTION OF THE DRAWINGS

The arrangement according to the invention will now be explained ingreater detail with reference to the following figures, of which:

FIG. 1 represents a double-glazed window suitable for application in thearrangement according to the invention;

FIG. 2A through 2D represents cross-section A--A of FIG. 1 inrespectively a first, second, third and fourth variant of thearrangement according to the invention;

FIG. 3 represents a single-pane window which can be used in thearrangement according to the invention;

FIG. 4 represents an embodiment, wherein a windowpane is provided with amotion sensor.

FIG. 1 shows a front view of a double-glazed window. Windowpane 1 andwindowpane 2 placed behind it are separated by spacer elements 3 fittedon all sides. The width 4 and height 5 of the windowpane shallpreferably be in the order of several tens of centimeters. As thedimensions are greater, the double-glazed window will be increasinglycapable of producing low tones. In the centre of the windowpane, a piezoelement 6, functioning as actuator, has been fitted to set windowpane 1and windowpane 2 into vibration with respect to one another. The piezoelement 6 can be provided with a varying voltage by means of twoconductors 7.

FIG. 2A represents cross-section A--A as shown in FIG. 1. For thepurpose of clarity, the distance 8 between the two windowpanes is shownsubstantially enlarged with respect to its normal proportion to thewidth 4 and the height 5. Usually, the distance 8 will not be more than1 or 2 cm. The windowpanes 1 and 2 are connected to the spacer elements3 by a coat of adhesive 9. The diameter 10 of the piezo element 6, whichin this case is cylindrical, is also in the order of 1 or 2 cm. Thepiezo element 6 is mechanically connected to the two windowpanes 1 and 2by means of a coat of adhesive 11. Each connector 7 is led down alongthe windowpane, through the spacer element 3, to be connected to theelectric signal generator 12. The piezo element 6 will then contract orexpand in accordance with the signal shape applied by the signalgenerator 12, which will cause windowpanes 1 and 2 to vibrate. In thisway, both windowpanes act as a loud speaker. In a feasible embodiment,one of the two windowpanes can be given an increased thickness andrigidity, as a result of which the other windowpane will be setvibrating. This provides a certain measure of directional sensitivity.If required, several piezo elements 6 can be provided to increase thesound pressure.

FIG. 2B represents cross-section A--A of FIG. 1 where piezo element 6has been omitted. In this situation, spacer elements 3 are used as piezoelements. This is a feasible solution if the central disposition of thepiezo element 6 is a nuisance visually. The spacer elements 3 are thenon two sides connected to the electric signal generator 12 viaconductors 13.

FIG. 2C represents cross-section A--A of FIG. 1 where piezo element 6 islikewise omitted. The actuator is then formed by conductive layers 14and 15 applied to the inside of windowpanes 1 and 2 in a vapourdisposition process. Conductive layers 14 and 15 are via conductors 16connected to an electric signal generator 17 which generates asufficiently high voltage to realize electrostatic attraction orrepulsion between both conductive layers. This will cause windowpanes 1and 2 to vibrate in accordance with the supplied signal shape.

FIG. 2D represents cross-section A--A of FIG. 1 where piezo element 6 islikewise omitted. The actuator consists of a gas confined in space 18between the two windowpanes 1 and 2. Via lead-through 19 provided in oneof the spacer elements 3 and a connecting line 20, space 18 communicateswith a pneumatic signal generator 21. The pressure in space 18 will thenvary in accordance with the signal shape supplied by pneumatic signalgenerator 21 and will set windowpanes 1 and 2 into vibration. In anotherembodiment, space 18 contains a liquid and signal generator 21 is ahydraulic signal generator.

FIG. 3 represents an arrangement according to the invention comprising asingle-pane window 22 which, by means of actuators 23, for instancepiezo elements, is connected to a frame 24. The actuators can, in amanner analogous to the method described above, be connected to anelectrical signal generator not shown here.

All above-described embodiments enable the signal generator to producean anti-sound signal. An extraneous sound signal acting on an enclosedspace can be recorded by means of microphones and be transmitted inphase opposition to the signal generator. This results in a substantialsound attenuation, particularly in the audio spectrum.

An alternative is to provide the space with one or several microphones,the signals of which can be applied to the signal generator, ifnecessary after application of a suitable filter. Any penetrating noisesignals can thus be adjusted to a minimum in a closed loop. Both methodscan also be applied in combination.

In a further favourable embodiment, the actuators are controlled in sucha way that the one windowpane or, in the case of multiple parallelwindowpanes, the inner windowpane motion is reduced to practically zero.The result of this is that no noise will enter the room via thatwindowpane. This can be effected by providing the inner windowpane witha sensor or a distributed set of sensors sensing the movement orabsolute position of the inner windowpane. The sensor signals can now beused by a control system to control the actuator, or a distributed setof actuators, thereby minimizing the motion of the inner windowpane. Inthis way, an effective noise dampening system is obtained. The usage ofa distributed set of actuators and a distributed set of sensors isparticularly advantageous in the case of higher frequencies, when thewindow tends to vibrate in higher modes. A distributed control anddampening of the window pane motion can thus be obtained.

An example of an embodiment wherein a window pane is provided with amotion sensor is given in FIG. 4, which is derived from the embodimentof FIG. 2B. The corresponding items in FIG. 4 are denoted with the samenumber as in FIG. 2B. In addition, windowpane 2 is provided with amotion sensor 25. The motion sensor may for example consist of two pairsof strain gauges appropriately glued on the windowpane. Alternatively,the motion sensor may consist of. a piezo electric transparent sheet.Preferably, the motion sensor 25 is applied where the windowpane motionhas a maximum, being in the middle of the windowpane, when the windowpane tends to vibrate at low frequencies in a base mode. Signals ofmotion sensor 25 are fed to controller 26. The controller 26 controlsthe signal generator 12, which generates the electrical signals forpiezo actuators 3, in such a way that the signals from motion sensor 25are minimized. The same principle can be applied, mutatis mutandis, forembodiments using a single windowpane and/or different types ofactuators.

I claim:
 1. A noise dampening system for dampening acoustic vibrationsentering a building via a window, comprising:a first substantially flatwindowpane; a second substantially flat windowpane parallel to the firstwindowpane, said first windowpane having a vibrational rigidity higherthan the second windowpane; an actuator configured to generate acousticvibrations in at least one of the first and second windowpanes; a sensorattached to the second windowpane and configured to sense motion of thesecond windowpane; and a control unit coupled to the sensor and theactuator, said control unit being configured to control the actuator tominimize the motion of the second windowpane using signals received fromthe sensor, said signals corresponding to the motion of the secondwindowpane sensed by the sensor.
 2. A noise dampening system as claimedin claim 1, wherein the actuator is mounted between the first and secondwindowpane.
 3. A noise dampening system as claimed in claim 2, whereinthe actuator comprises:a first conductive layer at least partiallyprovided on the first windowpane; and a second conductive layer at leastpartially provided on the second windowpane, said actuator beingactivated by a voltage difference between the first and secondconductive layers.
 4. A noise dampening system as claimed in claim 2,wherein the actuator comprises:a piezoelectric element positioned in thespace between the two windowpanes, said piezoelectric element beingmechanically connected to both windowpanes.
 5. A noise dampening systemas claimed in claim 1, wherein the sensor comprises:a plurality ofstrain gauges.
 6. A noise dampening system as claimed in claim 1,wherein the sensor comprises:a plurality of piezoelectric elements.
 7. Awindowpane arrangement, comprising:a first substantially flatwindowpane; a second substantially flat windowpane parallel to saidfirst windowpane, said first windowpane having a vibrational rigidityhigher than the second windowpane; an actuator configured to generateacoustic vibrations in at least one of said first windowpane and saidsecond windowpane; a sensor attached to the second windowpane andconfigured to sense motion of the second windowpane; and connectingmeans for connecting the sensor and the actuator to a control system forminimizing the motion of the second windowpane using signals receivedfrom the sensor, said signals corresponding to the motion of the secondwindowpane sensed by the sensor.